The present invention relates to a frame structure for a vehicle, in which a frame has a roughly rectangular main cross section which absorbs impact energy through its bending deformation in a vehicle collision.
Conventionally, passenger's protection in a vehicle head-on collision has been achieved by a structure in which an axially-crushable (deformable) crash can is provided at a tip portion of a high-tension steel-plate made front side frame and plural impact absorbing mechanisms which are bendable over a range from a middle portion to a rear end portion of the front side frame are provided (Japanese Laid-Open Publication No. 2009-137523). According to the impact absorbing mechanisms, an impact load absorbed through bending deformation of the front side frame occupies the most energy which has been absorbed, so that the energy-absorption characteristics of the bending deformation affects the EA (Energy Absorption) performance greatly more than the energy-absorption characteristics of the compressive deformation.
Accordingly, it can be considered to improve the strength and the EA performance against the bending by providing a sub closed cross section which is long in a bending direction inside the main closed cross section.
Herein, while the load to start bending of the frame is increased by providing a reinforcing member which forms the sub closed cross section, simply providing this reinforcing member delays the timing of starting the frame's bending in an initial stage of the vehicle collision, so that the collision impact (acceleration) acting on the vehicle may become improperly large temporarily. Also, the weight may increase improperly because the reinforcing member is large sized.